Boxing day is based on a Solstice holiday tradition that goes back to the Romans. On that day the servants and masters would switch place for the day, with the master doing the servants work while the servants would take over any of the master's responsibilities (often just relaxing). It was a kind of a 'servants appreciation day' if you will. Later the English, adopting the practice from the Romans, brought it on as one of the 12days of Christmas. Money and donations would be placed in a box and would be distributed from to the poor and less fortunate on Boxing Day. They would also often copy the Roman tradition of masters and servants switching places for the day in good fun. Servant jobs for the household would also get money or a bonus, often referred to as a Christmas box for the year of service. This is still often done by people at Christmas when you give a bonus tip to your Postman, Gardener/Lawn guy, paper boy, etc. There's and old episode of MASH that addresses the day https://youtu.be/3E17xEsi48g